Trickling filters, also known as bio filters, are normally a fixed-bed, biological reactor operating in aerobic conditions. In the filter, microorganisms are attached to the inter packing material which was composed of rocks or gravel in the past and is nowadays a wide range of plastic fill media. Fill media support is placed on the tank bottom with wide openings that allow a good air and water mixing.
Microorganisms on the fill media surface, work on the removal of soluble organic matter from the settled sewage that is sprayed over the bed surface trough a rotary distributor and is treated as it “trickles” through the fixed-bed, navigating through layers of microorganism. The layers remove pollutants by both absorption and adsorption removing species like nitrite, nitrate and others. Removal rates can reach up to 95%.
In order to avoid clogging, a primary sedimentation process precedes the trickling filter. Also, the design of the rotary distributor has a high impact on the risk of clogging. The rotation velocity of the rotary distributor can be changed by either adjusting the incoming water flow or by using an electrical motor. As smaller the rotation velocity as higher the water volume per square foot and as bigger is the flushing effect.
In time, the biofilm thickens and detaches into the liquid flow forming the secondary sludge. Trickling filters are normally followed by clarifier or sedimentation tanks. The sludge collected is treated for reuse or prior to disposal. Among the main advantages of this system it is important to highlight:
· The resistant to shock loadings
· High efficiency for ammonium oxidation
· Small land area required
· Final effluent is effectively stabilized
· The system is self-cleaning, operating with low maintenance requirements.
· Operational costs are low since wear and tear are reduced due to limited use of mechanical equipment.
Furthermore, in comparison with similar methods, such as activated sludge, trickling filters are significantly more cost-effective as they don’t require artificial aeration and have a smaller demand for operational space resulting in cost reduction.